1. Field of the Invention
The present invention relates to cameras and portable equipment with camera.
2. Related Background Art
Thin cameras that may be mounted on portable telephones with camera have shorter lens moving distance for focus and zoom adjustments in photographing compared to other ordinary cameras. For this reason, lens driving devices that magnetically drive the lens directly are suitable for use as lens driving devices applied to such cameras.
Among such lens driving devices of the magnetic drive type, the following, for example, are known. A lens driving device that has been suggested includes a cylindrical lens holder for holding a lens, a ring-shaped rotor magnet mounted on the outer circumference of the lens holder, and a drive coil that opposes the rotor magnet. By controlling the energization of the drive coil, the lens holder holding the lens is directly moved linearly in the optical axis direction to a predetermined position without the intervention of any conversion mechanism and magnetically held in the position.
Another type of lens driving device that uses a guide shaft that guides a lens holder holding a lens along the optical axis is known as an example of utilizing a conversion mechanism that converts a motor's rotational force into linear motion.
When taking a picture by a portable phone with camera, the portable phone is often held with one hand to take a picture of the holder's face or other subjects in close proximity. For this reason, photographic lenses used in this type of camera often have a close-up photographing function. In photographic lenses having such a close-up photographing function, the lens position for ordinary photographing and the lens position for close-up photographing, or macro photographing, are different. In other words, the lens position for close-up photographing is slightly closer to subject by a predetermined distance compared to the lens position for ordinary photographing.
As a result, this type of photographing lenses is provided with a driving source for moving the lens position between the ordinary photographing position and the macro photographing position, and the driving source is driven with a switch to move the lens between the two points of photographing positions. However, it is difficult to utilize a motor as a driving source on portable equipment such as portable telephones, due to the need to miniaturize the equipment and achieve lighter weight. Furthermore, since photographing takes place only in two positions, a lens driving device in which electromagnetic force is directly applied to the lens drive to move the lens is desirable.
However, in the conventional lens driving devices in which a lens holder is magnetically moved without a force conversion system, subtle positional controls that are required when executing zoom operations to enlarge or reduce an image are extremely difficult. Furthermore, since the drive coil is energized and excited to hold the lens holder in position, when the energization ceases, the lens holder is released from its position. Consequently, there is an additional problem of the lens position shifting as a result of external force and vibration when the energization ceases. On the other hand, always supplying power would result in large power consumption, which would make it impossible to mount the lens driving device on portable equipment such as portable telephones.
Moreover, in a lens drive mechanism in which rotational motion is converted into linear motion, although positional control during zoom operations is easy, the force transmission mechanism and conversion mechanism from the motor mechanism to the lens holder become complicated, which can result in poor assembly efficiency and a large device with a built-in lens drive mechanism.